Wait the US doesn't have an 'E'? (Is 'F' short for Fail? I thought it was just the continuation of the sequence). Regardless, at least A is best, B is worse than that, etc. which makes sense.
Well, apparently it's more complicated than that. I always assumed that the lack of E was so that there would be no confusion with the ESNU system (which a number of students used to have in elementary school, but then they switch over to the A-F system in middle school). Also, many countries outside the U.S., including non-english speaking ones, use the A-F system. Still researching the origin.
I had previously believed that the A-F system was universal across the US college system, though apparently University of Arizona has the 'E' grade.
http://www.jamesaltucher.com/2012/07/how-i-would-unschool-my...
A* to E, and then an actual failure is a U, so as to not just be a continuation from E I assume.